Pyrolytic reduction may be defined as the result of thermal decomposition of organic compounds in a reduced oxygen atmosphere. When organic molecules are heated to high temperatures, carbon-carbon sigma bonds rupture and the molecules are broken into free-radical fragments. This fragmentation step, called thermally-induced homolysis—which is homolytic cleavage caused by heat—is the initiation step for a series of free-radical reactions.
Controlled pyrolysis has traditionally been used in the petrochemical industry to achieve cracking of high-molecular weight compounds. For example, cracking crude oil at refineries. Such thermal cracking has been replaced with catalytic cracking which uses externally-applied heat in the presence of a catalyst.
Typically, pyrolytic scrap tire reduction may involve: i) subjecting the material for reduction to high temperatures from an externally applied heat source which may consume considerable amounts of energy, ii) processing the products of reduction, such as melted rubber, oil and char, which may require special handling for safety and transportation, and iii) combustion of reduction products at high temperatures which may result in additional environmental issues.
For example, combustion of scrap tires directly in a cyclone furnace or rotary kiln may result in: i) production of high levels of particulates, dioxins, carbon monoxide (CO), nitrogen oxides (NOx), sulfur oxides (SOx), and heavy metal vapors, ii) complex treatment of emissions products of combustion which may require the use of selective catalytic combustion, precipitators, or baghouses to reduce emissions to levels allowable under Environmental Protection Agency (EPA) regulations, and iii) disposal of residual waste products such as char, ash, and steel.